Human behavioral and physiological reactions to inhalation of sweet orange oil

Although essential oils are used increasingly for the improvement in quality of life as well as for the relief of various symptoms in patients, scientific evaluation of the effects of fragrances in healthy volunteers is rather scarce. Up to now, no experiments about the effects of sweet orange oil (Citrus sinensis) on human physiological parameters and on behavioral measures after inhalation have been carried out. Therefore, the main objective of the present study was to investigate the effects of this fragrance compound on physiological parameters as well as selfevaluation in healthy human subjects following inhalation. Physiological parameters recorded were blood pressure, breathing rate, skin temperature, and heart rate. Self-evaluation was assessed in terms of alertness, attentiveness, calmness, mood, relaxation, and vigour. Additionally, the fragrance was rated in terms of pleasantness, intensity, and effect. Sweet orange oil caused significant increases in heart rate as well as in subjective alertness, which are likely to represent a stimulating effect of the oil. These findings furnish scientific proof for the use of sweet orange oil in aromatherapy for the relief of mild forms of depression and stress in humans. INTRODUCTION Presently, the knowledge of the psychotherapeutic effects of fragrances has grown considerably. Especially in aromatherapy, Klemm et al. (1992) studied the human physiological responses to aromas. Their responses were assessed by EEG. All odors used affected the EEG in at least some subjects, and all subjects responded to at least some odors. Bursts of heliotropine (a vanilla-like scent) were administered to patients undergoing magnetic resonance imaging (MRI) and this reduced recalled anxiety by 63% in those who liked the smell (Redd et al., 1994). The effects of peppermint oil caused changes in brainwave patterns which were associated with alertness. In addition the peppermint aroma enhanced the sensory pathway for visual detection, which allowed the subjects more control over their allocation of attention (Parasuraman, 1991). Essential oils, i.e. Citrus lemon (lemon), Eucalyptus globulus (blue gum), Lavandula angustifolia (lavender), and Boswellia carteri (frankincense) were used for women with extensive severe burns (Price, 1989). For patients with Alzheimers, scented oils have the ability to act as a trigger and help them recapture some of their past experiences (Brett, 1997). Although essential oils are used increasingly for the improvement of the quality of life as well as for the relief of various symptoms in patients, scientific evaluation of the effects of fragrances in healthy volunteers is rather scarce. Up to now, no experiments about the effects of sweet orange oil on human physiological parameters and on behavioral measures after inhalation have been carried out. Therefore, the main objective of the present study was to investigate the behavioral and physiological reactions to sweet orange oil in healthy human subjects following inhalation. Proc. WOCMAP III, Vol. 5: Quality, Efficacy, Safety, Processing & Trade in MAPs Eds. E. Brovelli, S. Chansakaow, D. Farias, T. Hongratanaworakit, M. Botero Omary, S. Vejabhikul, L.E. Craker and Z.E. Gardner Acta Hort. 679, ISHS 2005 76 MATERIALS AND METHODS Subjects and Fragrance Compounds Twenty-four (12 males and 12 females) healthy volunteers between the ages of 19 and 23 years (mean age 21.38 ± 1.21 years) took part in the experiments. They were recruited by advertisement at Srinakharinwirot University. Subjects were tested in individual sessions and randomly assigned to either the control group or the sweet orange oil group. Each group consisted of 12 subjects (6 males and 6 females). Twenty-four hours prior to testing subjects had to abstain from food and beverage containing the substances tested, e.g. Oranges, Lemons, Ceylon cinnamon, Sassafras, Eucalyptus, Caraway, Fennel, Chewing gum, as well as from tea, coffee, and alcoholic beverages. Sweet orange oil (Citrus sinensis) was obtained from FPI Sale Ltd., Stamford, England. The oil contains up to 98% of the monoterpene limonene. Fragrance Administration The fragrance and a placebo substance were administered by inhalation via an aroma lamp, consisting of a candle and a small ceramic bowl. In the experimental group the small ceramic bowl was filled with the fragrance and pure water. In the control group it was filled with only pure water. 1.2 g sweet orange oil in 3.5 g pure water was used in the experimental group, while 5 g pure water was used in the control group. Experimental Design The experimental design is shown in Fig. 1. One session consisted of two trials of 20 minutes each. At the beginning and end of each trial subjective mental and emotional condition was assessed by visual analogue scales (VAS). Physiological parameters were recorded continuously during each trial. Blood pressure was measured at the beginning as well as at the end of each trial. In the first trial, which served as a control for influences of the experimental setup, the placebo substance was administered to all subjects. In the second trial the placebo was again administered to the control group, whereas in the experimental groups the appropriate fragrance was administered. Acquisition of Physiological Parameters Breathing rate (BR), heart rate (HR), and skin temperature (ST) were recorded simultaneously and in real time. All parameters were measured using Power Lab/4SP hardware (ADInstruments, Inc., NSW, Australia). Sampling rate was 100 Hz. Heart rate was assessed employing a Bio Amplifier (ML132) and a disposable ECG electrode (MLA1010). Skin temperature was measured by means of a Bridge Amplifier (ML110) and a skin temperature transducer (MLT409). Breathing rate was measured using a Bridge Amplifier (ML110) and the nasal temperature probe (MLT415) which registers breathing cycles on the basis of the difference in temperature between inhaled and exhaled air. Systolic and diastolic blood pressure (SBP and DBP) were measured in the dominant arm by sphygmomanometry using an automated system (Digital Electronic Model DS-155E, Japan). SBP and DBP were measured four times throughout the experiment. Visual Analogue Scales (VAS) VAS were used to assess subjective mental and emotional condition. They consisted of 100 mm lines for six items: relaxation, vigor, calmness, attentiveness, mood and alertness. Each subject was asked to mark his or her feeling for each item between the two possible extremes. Procedure All experiments were conducted in a bright and quiet room. Ambient temperature was 24-26°C. Upon arrival, the volunteers were interviewed about their personal data, i.e. name, age, sex, weight and height. In addition, they were asked about the rating of mental